Diseases of The Knee

The last chapter mentioned some of the potential problems that can be associated with specific anatomical features of the knee. Like the hip, some categories of knee problems are broader, and these need specific discussion.

This chapter discusses the most common types of arthritis and other common causes of knee pain, such as meniscal tears, bursitis, osteochondral lesions, and avascular necrosis. Another important cause of knee pain is actually hip joint problems; hip arthritis commonly can present as knee pain. It is not unusual to see a patient who reports they have been told x-rays of his knee are fine, but that he has serious knee pain and limitation, only to find a hip x-ray shows significant pathology in his hip!

Osteoarthritis of the Knee

Advanced arthritic changes of the knee, viewed from above. Note the worn areas over the joint contact surfaces and the frayed meniscus. Osteoarthritis, or the "wear and tear" variety of arthritis, is probably the most common reason for knee pain in mature adults. It is certainly the problem that I see most commonly with patients aged 50 or older who report pain that has been present for longer than several months, although it is by no means the only cause for such pain. It also can be seen in patients of much younger age, especially in obese patients.

The articular cartilage is a coating of smooth, soft cartilage about 1/8th inch thick covering the ends of the femur, tibia, and patella undersurface. As mentioned in the last chapter, it can wear away with time or injuries, and after skeletal maturity it does not grow back.

There definitely appears to be a genetic predisposition to developing osteoarthritis.

Frequently, one of the compartments of the knee (usually the medial, or inner side of the knee) may wear out sooner than the other compartments. In this case, some options are available for treatment that are not useful when all three compartments are affected, such as orthotics, off-loader braces, and partial knee replacements. These options for single compartment disease will be discussed more fully in the next couple of chapters.

As the cartilage covering begins to wear away, underlying bone surfaces are eventually exposed (hence the common term "bone on bone" arthritis). As the process continues, the body responds by making osteophytes (large spurs) around the peripheral edges of the joint and often by making more joint fluid. This can result in a large joint effusion, or "water on the knee," which sometimes needs to be drained. The knee will also usually become progressively more stiff as the process continues, and frequently an angular deformity may develop as one side wears out faster than the other. This commonly results in a varus (or "bow-legged") appearance, although sometimes it can result in a valgus (or "knock kneed") deformity. A flexion contracture may eventually develop in which the knee no longer can fully straighten out.

 

 

 

 

 

Trauma And Post-Traumatic Arthritis

There are numerous traumatic injuries that can occur in the knee, ranging from contusions and bone bruises to fractures involving the joint surface or nearby shafts of the tibia or femur. Trauma can result in injury to any of the ligaments of the knee or even to multiple ligaments, each requiring treatment that varies from simple bracing and observation (such as a partial medial collateral ligament injury) to extensive reconstruction surgeries (such as an ACL reconstruction). There is a wide variation in treatments of acute injuries, and we will not be able to discuss those in detail here as this book is primarily dedicated to joint replacement and related surgeries.

However, it is important for our discussion here to understand that post-traumatic arthritis can develop after injuries to the knee, and clinically it looks and is treated similar to osteoarthritis. It is not uncommon for patients who have had prior traumatic injuries to the knee to develop post-traumatic arthritis years later. A large percentage of patients who sustain tibial plateau fractures (fractures that involve the weightbearing surface of the tibia) require knee replacement surgeries in the years after the injury, despite adequate bone healing with plates and screws after the initial injury. The smooth surface of the joint becomes disrupted, and over time arthritis results.

For many years, the standard treatment for meniscal tears involved resecting the entire meniscus from the affected side of the knee. However, it turns out that the meniscus serves an important function as a stabilizer for the knee, and without it most people develop severe arthritis in the knee over the years after excision. After the development of arthroscopic surgery, complete meniscectomies became rare, and most surgeons treat nonhealing meniscal tears with arthroscopic surgery in which only the torn portion of the meniscus is removed (and sometimes repaired, if possible). However, it is common to see patients who had complete meniscectomies (or removal of "torn cartilage in the knee") years ago who now require partial or total knee replacement.

Rheumatoid Arthritis

As discussed in the section on hips, another large category of arthritis is that of autoimmune arthritis. These types of arthritis are primarily the result of the body's own immune system attacking the joints, rather than "wear and tear" osteoarthritis, and the most familiar of these is rheumatoid arthritis. Other related "inflammatory" arthropathies include psoriatic arthritis (from psoriasis), lupus, and other rheumatologic diseases.

Frequently patients with these types of arthritis have systemic involvement in which multiple joints are large, swollen, red, and painful. Most frequently the joints of the hands are affected first, but not all patients have that initial presentation. Since newer treatments became available in the last decade or so, we are seeing fewer patients with this type of arthritis who need joint replacement early on.

The synovial lining of the joint often becomes inflamed, red, and boggy with rheumatoid arthritis. Often the inflammation of the lining can be destructive to the joint itself, leading to loss of cartilage and bone over time.

The majority of patients with rheumatoid arthritis (and related arthritic types) are already diagnosed by the time they reach the orthopaedic surgeon, but not always. Blood tests are somewhat helpful but not always definitive in diagnosis of these disorders. Evaluation by a rheumatologist is sometimes needed.

Because of the nature of the disease, tendons and ligaments may rupture over time as the body attacks these tissues. This is why patients with advanced rheumatoid arthritis often have gnarled, deformed hands as the tendons become involved. It is also the reason why many surgeons recommend using a posterior stabilized knee replacement that replaces the posterior cruciate ligament when replacing knees in patients with rheumatoid arthritis, whether or not the patient currently has symptoms with it, because the PCL is prone to rupture in the setting of untreated rheumatoid arthritis.

Osteochondral Defects / Loose Bodies

Arthroscopic photo of an osteochondral defect. The probe is in the center of a defect - similar to a pothole - in the cartilage surface of the knee. The articular cartilage surface in the knee, like most joints, resembles a smooth Teflon coating that can wear away over time. Sometimes "potholes" can develop in the surface of the joint, and these can definitely be seen with arthroscopic surgery when the camera is inserted into the joint for a look around. Sometimes a plug of cartilage and underlying bone can break loose, leaving a crater in the normally smooth surface. This crater by itself is harmful, and often leads to accelerated arthritis, but the chunk of bone and cartilage (hence the term osteochondral) can be even more painful and destructive. The loose chunk can become a loose body, moving around inside the knee joint and causing damage, frequently leading to mechanical problems such as catching and locking as the loose piece becomes caught in the knee.

 

 

 

Chondromalacia

Somewhere along the spectrum between normal joint cartilage and "bone on bone" arthritis in which it is absent, the cartilage goes through a time when it is soft and begins to "delaminate" or peel away. This phase is often referred to as chondromalacia, and it can be seen even in young patients. It does not necessarily mean that serious arthritis is eminent, although it often is a sign of probable degenerative changes that can be expected later.

Surgeons often grade the degree of chondromalacia during arthroscopic surgery, when the joint surfaces can be closely examined with the camera and photographed. These range from minimal cartilage "blistering" to large areas of exposed, denuded bone with the overlying cartilage completely worn away. Consequently, surgeons can often advise patients of the status of the joint after arthroscopic surgery and may forecast the need for knee replacement in the future.

 

Meniscal Tears

As mentioned in the last chapter on knee anatomy, the menisci are "C"-shaped sections of cartilage (similar to that in the nose and ears) that form gaskets in the knee. There are two of these gaskets, one on each side of the knee. The meniscus on the medial side, or inner knee, is most frequently affected by tears. Tears can come in a variety of shapes and sizes, ranging from small tears that heal on their own without intervention to large, "bucket-handle" tears that cause the knee to lock, catch, or buckle.

Many meniscal tears result from a twisting injury to the knee, and patients may recall the moment that it occurred and feeling a "pop" as the meniscus tore. Many other patients do not recall the injury at all, often because the pain and swelling may not be problematic until hours or days after the injury. Still other patients develop degenerative tears, in which the fibers begin to fray like a rug that has been walked on too many times, and describe gradual pain and symptoms over time.

Most patients report pain as the principal problem when a meniscal tear develops. Patients with large tears experience mechanical symptoms of internal derangement, such as a catching or popping sensation when the knee flexes and extends. Large tears can cause the knee to painfully lock as the torn fragment becomes trapped in the hinge of the knee. Most patients find that squatting becomes very difficult, and flexing the knee far back (more than 110 degrees) becomes painful.. The knee may or may not swell, depending on the acuity of the injury.

A Baker's cyst may form in the back of the knee (in the space known as the popliteal fossa), often in relation to meniscal problems. It is common for a Baker's cyst to be identified on an MRI or ultrasound, and patients are often unnecessarily alarmed about the abnormality on their report. Although the pain that patients feel is often in the same area, the cyst itself often is not truly the source of the problem. It is uncommon that cysts are treated surgically, and they often resolve over time after the meniscal tear or underlying pathology has been dealt with (either surgically or by healing on its own). On occasion, the cysts can become quite large, particularly in rheumatoid arthritis patients, and these sometimes are dealt with surgically. Cysts can also rupture, which is usually harmless but may cause a disconcerting sensation of warm water running down the back of the calf.

It is important to note that most patients with significant arthritic changes also have meniscal tears. As the surfaces of the joint become rougher, the cartilage meniscus between becomes torn and ground away. For this reason, orthopaedic surgeons usually do not find an MRI helpful in evaluating a knee that is clearly arthritic on x-rays, as meniscal tears are expected.

Avascular Necrosis (Osteonecrosis)

As discussed in the section of the book on hip diseases, avascular necrosis (or osteonecrosis, as it is sometimes called) is a process in which a portion of the bone around the joint begins to die. This usually occurs because of poor blood flow to the affected area of bone, and the underlying causes for this are many. Coagulation problems and injury are common factors, but many patients develop the disease for no identifiable reason.

As the area of bone begins to die, the overlying joint surface may collapse, similar to a sinkhole. The process is painful and most patients seek medical treatment before it reaches the point of collapse. The most commonly affected area is the femoral condyle, or the end of the thigh bone, although the disease can also be seen in the upper end of the tibia. If the area collapses, severe degenerative changes will ensue quickly that resemble (and are treated similarly to) severe arthritis.

The process can sometimes resolve on its own before collapse occurs, however, with activity modification and conservative management. Some surgeons advocate limited or no weightbearing using crutches, a walker, or an off-loader brace (which redistributes the load to the opposite side of the knee). Other potential treatments can include arthroscopic drilling, which is sometimes successful in arresting the process.

Infection

Infection of the knee is a relatively uncommon cause of chronic knee pain. It typically presents with an acute infection (sepsis), with purulent material in the knee that necessitates emergency surgery to "wash out" the joint. Patients are usually quite ill with high fevers, inability to move the knee, and severe swelling and pain. It occurs most often in patients who have a compromised immune system (including diabetics) or a reason to have introduced bacteria into the knee joint (such as a penetrating wound or an infected diabetic ulcer lower down the leg).

In unusual cases, a chronic low-grade infection is another potential cause, often from Lyme Disease or similar diseases. A blood test usually reveals infection by these types of bacteria. Aspirating (e.g., drawing fluid out of the knee with a needle) and sending the joint fluid for testing is also helpful in diagnosing infections in the joint.

Knee Bursitis / Tendinitis

Not all from knee pain arises from problems within the joint itself. The tendons around the knee can develop inflammation (e.g., "jumper's knee") and in severe cases the quadriceps or patella tendons can rupture, requiring surgical repair. Tendinitis usually resolves with conservative treatment consisting of activity modification and physical therapy.

There are several bursae around the knee joint as are found around other large joints in the body. The prepatellar and pes anserine bursa are most commonly affected. These fluid-filled sacs help muscle layers slide smoothly over each other, but the sac can sometimes become inflamed and painful. Sometimes it can fill with fluid that needs to be drained. Bursitis often resolves with steroid injections, anti-inflammatory medications, and physical therapy.

Ligamentous Injuries

The four primary ligaments in the knee are the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments. Basically, each of these ligaments prevents the knee from traveling in one direction (either side to side or backwards and forwards). These ligaments can often be sprained, especially in sports injuries, and these minor injuries usually heal without any intervention beyond bracing and other conservative treatment.

However, some sports injuries can result in complete disruption of one (or occasionally multiple) ligaments. Collateral ligament injuries (the ones on the sides of the knees) may heal with the use of a brace and without the need for surgical repair. Anterior or posterior cruciate ligament (ACL or PCL) injuries are different, however, and complete tears usually do not heal on their own. In fact, simply suturing the ligaments back together (as was tried in the past) usually is not adequate either, and these ligaments usually require reconstruction surgeries using tendons harvested from other body sites (commonly the patella tendon or the hamstrings) or from cadaver tissue.

ACL and PCL reconstruction surgeries have a significant rehabilitation period afterwards. However, not all patients elect to have reconstruction surgery performed. If a patient is not actively participating in sports, they may find that the occasional instability with stairs or unlevel surfaces is something they can live with and many may decide that reconstruction surgery is not for them. Young patients or athletes, on the other hand, often opt for reconstruction surgery with an orthopaedic surgeon specializing in sports medicine.

Please remember the information on this site is for educational purposes only and should not be used to make a decision on a condition or a procedure. All decisions should be made in conjunction with your surgeon and your primary care provider.